1. Field of the Invention
This invention relates to a rotation phase control device for synchronizing the rotation phase of the rotor of a motor with a reference signal and more particularly to a rotation phase control device provided with a steady-state characteristic compensating circuit.
2. Description of the Prior Art
For a motor to rotate at a constant speed and a constant phase, the speed and phase of rotation of the motor are generally unvarying and are controlled by means of a speed control loop and a phase control loop with these control loops arranged for the motor. In this instance, to compensate for the steady-state characteristic of the phase control loop, previously either a lug-lead type loop filter which consists of resistors R1 and R2 and a capacitor C as shown in FIG. 1A of the accompanying drawings was inserted into the input stage of an error amplifier A or a lug type loop filter which consists of a resistor R2 and a capacitor C as shown in FIG. 1B was inserted into the feedback loop of an error amplifier A. The phase error at a steady-state can be reduced by the addition of the loop filter as shown in FIG. 1A or FIG. 1B, because it is possible to increase a gain within a low zone to a degree without impairing a phase allowance in a high zone.
However, the phase control loop with the above-described construction has a time constant (CR) and therefore deteriorates the starting characteristic of the motor.
The steady-state characteristic of a motor is generally inversely proportional to the starting characteristic thereof. Therefore, the starting characteristic is deteriorated as the steady-state characteristic is improved.
It is therefore a principal object of this invention to provide a novel rotation phase control device which is capable of eliminating the above-stated shortcoming of the prior art device and to provide a servo control device employing the rotation phase control device.
It is another object of the invention to provide a novel rotation phase control device which is capable of improving the starting characteristic of a motor by very simple means without deteriorating the steady-state characteristic of the motor and to provide a servo control device employing the rotation phase control device.
These and further objects and features of the invention will become apparent from the following detailed description of a preferred embodiment thereof taken in conjunction with the accompanying drawings.